Patent Application
20070095053
The present disclosure relates to methods and apparatus for removal of emissions from exhaust gas.
There are emissions traps used to trap emissions in an effort to prevent discharge of the emissions into the atmosphere. From time to time, these traps need to be regenerated to remove the emissions trapped thereby for further use of the traps.
According to an aspect of the present disclosure, there is provided an apparatus comprising an emissions trap and a trap regenerator. The trap regenerator is fluidly coupled to the emissions trap to advance a regenerative agent thereto to regenerate the emissions trap. The trap regenerator is configured to change a concentration of the regenerative agent advanced to the emissions trap from a first trap-regenerating level to a second trap-regenerating level different from the first trap-regenerating level. In this way, the amount of emissions discharged into the atmosphere can be reduced. An associated method is disclosed.
The emissions trap may be any one of a number of different types of emissions traps. For example, the emissions trap may be configured as a NOx (i.e., nitrogen oxides) trap, a sulfur trap, and/or an ammonia trap, to name just a few.
The above and other features of the present disclosure will become apparent from the following description and the attached drawings.
While the concepts of the present disclosure are susceptible to various modifications and alternative forms, specific exemplary embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the disclosure to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives following within the spirit and scope of the invention as defined by the appended claims.
Referring to
It is believed that trap regeneration may be a two-step process involving (1) release of emissions from the trap 12 (i.e., desorption), and (2) conversion of the released emissions to a more environmentally acceptable form. In some cases, the conversion rate may occur more slowly than the release rate at least for some initial period of time during trap regeneration. In such a case, this could result in undesirable spikes in the amount of unconverted emissions discharged into the atmosphere.
To address this issue, the trap regenerator 16 may be operated to slow the release rate during this initial period of time. In particular, the trap regenerator 16 may be operated to provide the first trap-regenerating level to the trap 12 during a first period of time and the second-trap regenerating level to the trap 12 during a second period of time subsequent to (e.g., immediately or shortly after) the first period of time, the first and second trap-regenerating levels being selected so that the release rate during the first period of time is slower than the release rate during the second period of time. Upon expiration of the first period of time, the conversion rate is able to “handle” the faster release rate of the second period of time, thereby allowing an increase in the overall speed of trap regeneration during the second period of time.
Illustratively, the trap regenerator 16 comprises at least one component 18 configured to provide at least a portion of the regenerative agent and an electronic controller 20 electrically coupled to the at least one component 18. The controller comprises a processor 22 and a memory device 24 electrically coupled to the processor 22. The memory device 24 has stored therein a plurality of instructions which, when executed by the processor 22, cause the processor 22 to operate the at least one component 18 in a first mode establishing the first trap-regenerating level, and operate the at least one component 18 in a second mode establishing the second trap-regenerating level.
The emissions trap 12 may be embodied as any number of different types of emissions traps. For example, the trap 12 may be, but is not limited to, a NOx trap for trapping NOx present in exhaust gas of the engine 14, a sulfur trap for trapping sulfur (e.g., in the form of SOx, sulfur oxides) present in the exhaust gas, and/or an ammonia trap for trapping ammonia that may have been introduced into the exhaust gas to facilitate reduction of NOx at a selective catalytic reduction device.
A fuel-rich environment may be created about the emissions trap 12 to regenerate the trap 12. This is particularly useful where the emissions trap 12 includes a NOx trap, a sulfur trap, and/or an ammonia trap. As such, the regenerative agent may have an air-to-fuel ratio and the trap regenerator 16 may change the air-to-fuel ratio from the first trap-regenerating level to the second trap-regenerating level, both trap-regenerating levels being fuel-rich. To change the air-to-fuel ratio from the first trap-regenerating level to the second trap-regenerating level, the amount of exhaust gas (which contains O2) and/or fuel supplied to the trap 12 can be varied in a variety of ways (discussed in more detail below). What is meant herein by the term “fuel-rich” is that the air-to-fuel ratio is less than the stoichiometric air-to-fuel ratio of the fuel (stated quantitatively, the lambda value of a fuel-rich mixture is less than 1.0).
Considering for a moment the particular case where the trap 12 is a NOx trap, it is believed that NOx-trap regeneration is a two-step process involving (1) release of NOx from the trap 12 (i.e., NOx desorption), and (2) chemical reduction of the released NOx to N2 by a NOx reductant of the regenerative agent. During NOx trap regeneration, NOx is released from the surface nitrate storage sites faster than it is initially reduced to N2 by reaction with the reductant, which, in some cases, may result in spikes in the amount of NOx discharged to the atmosphere. As such, the trap regenerator 16 may be operated so that, although both trap-regenerating levels is fuel-rich to effect NOx reduction, the first trap-regenerating level is less fuel-rich than the second trap-regenerating levels. As a result, the NOx-release rate is slower during the first period of time than during the second period of time, allowing the NOx-reduction rate time to increase to an amount to handle the increased NOx-release rate of the second period of time. In this way, the amount of NOx discharged into the atmosphere during a trap regeneration event can be reduced.
Referring to
Illustratively, the regenerator 116 may include an air valve 26, a fuel injector 28, and/or a fuel reformer 30 electrically coupled to and under the control of the controller 20 to change the air-to-fuel ratio of the regenerative agent supplied to the trap 12. The controller 20 may be electrically coupled to the air valve 26, the fuel injector 28, and the fuel reformer 30 via electrical lines 32, 34, and 36, respectively.
The air valve 26 may be, for example, the throttle valve that controls the amount of air introduced into the engine 14. In such a case, the position of the air valve 26 may be varied to change the amount of 02 in, and thus the air-to-fuel ratio of, the exhaust gas that flows to the trap 12.
The fuel injector 28 may be, for example, one or more of the fuel injectors that injects fuel into the engine 14. In such a case, the position of the fuel injector 28 may be varied to change the amount of fuel in, and thus the air-to-fuel ratio of, the exhaust gas that flows the to the trap 12.
The fuel reformer 30 may be used to dose the exhaust gas with a reformate gas comprising, for example, hydrogen (H2) and/or carbon monoxide (CO) so as to change the air-to-fuel ratio provided to the trap 12. In the case where the trap 12 is a NOx trap, such fuel acts as a NOx reductant.
The air valve 26, the fuel injector 28, the fuel reformer 30, or any combination thereof may be included in the trap regenerator 116 to change the air-to-fuel ratio of the regenerative agent advanced to the trap 12.
Referring to
Illustratively, there are two emissions traps 12a and 12b positioned in a dual-leg arrangement of the exhaust system. The first trap 12a is positioned in a first leg 38 and the second trap 12b is positioned in a parallel second leg 40. As such, the traps 12a, 12b are flow-parallel to one another.
An exhaust valve arrangement is used to control flow of the regenerative agent to the traps 12a, 12b. The regenerative agent comprises exhaust gas from the engine 14, or more particularly the O2 present therein, and a reformate gas (e.g., H2 and/or CO) generated by the fuel reformer 30. In the case where the trap 12a or 12b is a NOx trap, the reformate gas acts as a NOx reductant. The exhaust valve arrangement is thus configured to control flow of the exhaust gas and the reformate gas to the traps 12a, 12b.
Illustratively, the exhaust valve arrangement comprises a first exhaust valve 52, a second exhaust valve 54, and a third exhaust valve 56. The first exhaust valve 52 is positioned upstream from the traps 12a, 12b at an upstream junction of the legs 38, 40 so as to be able to control flow of exhaust gas and the agent component to the traps 12a, 12b. The second exhaust valve 54 is positioned in the first leg 38 downstream from the first trap 12a. The third exhaust valve 56 is positioned in the second leg 40 downstream from the second trap 12b.
The controller 20 is electrically coupled to each valve 52, 54, 56 and the fuel reformer 30 via electrical lines 58, 60, 62, 36, respectively, to control operation of these components and thus regeneration of the traps 12a, 12b. Normally, both traps 12a, 12b are “on-line” such that they trap emissions present in exhaust gas advanced through both traps 12a, 12b. To establish this configuration, the first exhaust valve 52 is positioned to allow exhaust gas to flow to both legs 38, 40 and each of the second and third exhaust valves 54, 56 is opened the position shown in solid in
As alluded to above, each trap 12a, 12b is regenerated in two phases, the first phase occurring during a first period of time and the second phase occurring during a second period of time subsequent to the first period of time. In the first phase (i.e., during the first period of time), the first trap-regenerating level is advanced to the trap 12a, 12b, and, in the second phase (i.e., during the second period of time), the second trap-regenerating level is advanced to the trap 12a, 12b.
Each of the valves 52, 54, 56 allows a certain amount of exhaust gas to leak past it even when it is “closed.” More particularly, the first exhaust valve 52 has a higher leakage rate than each of the second and third exhaust valves 54, 56. Exemplarily, the first exhaust valve 52 may allow about 3% leakage when it assumes either the solid or phantom position shown in
To regenerate the first trap 12a while the second trap 12b remains on-line, the controller 20 signals the first exhaust valve 52 to move to the position shown in solid in
The controller 20 operates the second exhaust valve 54 to establish the first and second trap-regenerating levels of the first and second phases of trap regeneration. In particular, in the first phase, the controller 20 signals the second exhaust valve 54 to assume its opened position shown in solid in
Upon expiration of the first period of time, the controller 20 signals the second exhaust valve 54 to assume its “closed” position shown in phantom in
A process similar to what has just been discussed in connection with the regeneration of trap 12a may be used to regenerate trap 12b. In particular, the controller 20 signals the first exhaust valve to assume the position shown in phantom in
In some embodiments, the second and third valves 54, 56 may be eliminated. In such a case, the first exhaust valve 52 may be variable in the sense that its position can be varied in small amounts by the controller 20 so as to change the leakage rate of exhaust gas into a leg 38, 40 from the higher leakage rate (e.g., 3%) establishing the first trap-regenerating level to the lower leakage rate (e.g., 1%) establishing the second trap-regenerating level. The first exhaust valve 52 may be, for example, a proportional valve. In other examples, a stepper motor or other valve actuator may be used to vary the position of the valve 52 in this way.
In other embodiments where the second and third valves 54, 56 have been eliminated, the controller 20 may vary operation of the fuel reformer 30 while the first exhaust valve 52 remains stationary. In other words, the amount of reformate gas may be varied while the leakage rate of exhaust gas past the valve 52 is generally fixed. In such a case, the fuel reformer 30 may be operated to produce more reformate gas during the second phase than during the first phase to establish the first trap-regenerating level during the first phase and the more fuel-rich second trap-regenerating level during the second phase. It is within the scope of this disclosure to control the fuel-richness of the regenerative agent by a combination of varying the leakage rate of exhaust gas into the respective leg 38, 40 and varying the amount of reformate gas supplied by the fuel reformer 30.
In still other embodiments, the second NOx trap 12b and the third exhaust valve 56 may be eliminated from the apparatus. In such a case, the second leg 40 may act simply as a bypass of the first leg 38.
The fuel reformer 30 may be configured in a variety of ways. For example, it may include a catalytic reformer and/or a plasma fuel reformer. A catalytic reformer may be embodied as any of a steam reformer catalyst, a partial oxidation catalyst, and/or a water-shifting catalyst, to name just a few. A plasma fuel reformer generates an electrical arc (i.e., a plasma) to initiate partial oxidation of a fuel (e.g., diesel, gasoline) into reformate gas including, for example, H2 and/or CO. In some cases, the fuel reformer 30 may include a combination of a plasma fuel reformer and a catalyst.
It is to be understood that the fuel reformer 30 may be replaced by a fuel source in any of the regenerators 16, 116, 216. As such, the fuel source may supply fuel (rather than reformate gas) such as diesel fuel, gasoline, etc. for use in regeneration of the traps.
The duration of the first period of time and the second period of time may depend on a number of factors (e.g., trap composition, final air-to-fuel ratio of interest). Exemplarily, each of the first and second periods of time may be on the order of 1 to 5 seconds.
While the concepts of the present disclosure have been illustrated and described in detail in the drawings and foregoing description, such illustration and description is to be considered as exemplary and not restrictive in character, it being understood that only illustrative embodiments have been shown and described and that all changes and modifications that come within the spirit of the disclosure are desired to be protected.
There are a plurality of advantages of the concepts of the present disclosure arising from the various features of the systems described herein. It will be noted that alternative embodiments of each of the systems of the present disclosure may not include all of the features described yet still benefit from at least some of the advantages of such features. Those of ordinary skill in the art may readily devise their own implementations of a system that incorporate one or more of the features of the present disclosure and fall within the spirit and scope of the invention as defined by the appended claims.
